Rotary drilling methods employing a drill bit and drill stems have long been used to drill wellbores in subterranean formations. Drilling fluids or muds are commonly circulated in the well during such drilling to cool and lubricate the drilling apparatus, lift cuttings out of the wellbore, and counterbalance the subterranean formation pressure encountered. Drilling fluids and muds often contain entrained solids which have been purposefully added, such as: weighting agents, such as barite, hematite, aluminite, and the like; viscosifying agents including sepolite clay, and other viscosifying clays; and fluid loose control agents, etc. . . . as well as very fine solid particles generated by the drilling process. Unlike drill cuttings, these entrained solids are difficult to remove by screening. However, upon standing, the solids often settle out over long periods of time (i.e. hours to days). Thus when the used drilling fluids or muds are being stored in tanks awaiting transport for recycling, these entrained solids typically settle out into the bottom of the tank and form a dense layer of solids.
Removal of the settled entrained solids from the bottom of a tank has proven to be a difficult problem. The current state of the art is to have a crew of at least two men enter the drained tank and using high pressure washing equipment and vacuums, wash and remove via vacuum the dense layer of solids. Such operations are both time and labor intensive and involve placing people inside of large storage tanks which raises certain safety concerns. One alternative has been to use tanks with a steep conical sidewall shape which helps prevent the settling of the solids. However, such tanks are expensive and an inefficient use of space on an offshore drilling rig or drilling rig service boat.
Thus there exists an ongoing need for improvements in the apparatus and methods used to clean tanks of sediments and solids deposited in them.